Golf ball cover compositions

ABSTRACT

The present invention is directed to golf ball cover compositions containing blends of high or low carboxylic acid based copolymers and ethylene copolymers such as ethylene alkyl acrylates. The carboxylic acid groups of the blends are neutralized with metal cations. Golf balls produced with the cover molded thereon exhibit desired properties of distance and high coefficient of restitution without substantially sacrificing and/or improving characteristics like playability and durability when compared to existing covers comprising ionomeric resin blends.

FIELD OF THE INVENTION

The present application is a continuation of U.S. application Ser. No. 08/359,620 filed on Dec. 20, 1994 U.S. Pat. No. 5,542,677.

The present invention relates to metal cation neutralized blends of acid copolymers with non-acid functional polymers such as ethylene acrylates, and to improved golf ball covers made from these blends. The improved golf ball covers are useful for producing golf balls, particularly multi-piece balls, exhibiting essentially the desired travel distance while maintaining or improving the playability and/or durability characteristics necessary for repetitive play.

BACKGROUND OF THE INVENTION

Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability, and flight characteristics, various ionomeric resins sold by E.I. DuPont de Nemours & Company under the trademark "Surlyn®" and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks "Escor®" and the tradename "Iotek", have become the materials of choice for the construction of golf ball covers over the traditional "balata" (trans polyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability properties required for repetitive play.

Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid or maleic acid. In some instances, an additional softening comonomer can also be included to form a terpolymer. The pendent ionic groups in the ionomeric resins interact to form ion-rich aggregates contained in a non-polar polymer matrix. The metal ions, such as sodium, zinc, magnesium, lithium, potassium, calcium, etc. are used to neutralize some portion of the acid groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. improved durability, etc. for golf ball construction over balata.

Broadly, the ionic copolymers comprise one or more alpha-olefins and from about 9 to about 30 weight percent of alpha, beta-ethylenically unsaturated mono- or dicarboxylic acid, the basic copolymer neutralized with metal ions to the extent desired. Usually, at least 20% of the carboxylic acid groups of the copolymer are neutralized by the metal ions (such as sodium, potassium, manganese, zinc, lithium, calcium, nickel, magnesium, and the like) and exist in the ionic state. In general, ionic copolymers including up to 16% acid are considered "low acid" ionomers, while those including greater than 16% acid are considered "high acid" ionomers by the present inventors.

Suitable olefins for use in preparing the ionomeric resins include ethylene, propylene, butene-1, hexene-1, and the like. Unsaturated carboxylic acids include acrylic, methacrylic, ethacrylic, α-chloroacrylic, crotonic, maleic, fumaric, itaconic acids, and the like. The ionomeric resins utilized in the golf ball industry are generally copolymers of ethylene with acrylic (i.e. Escor®) and/or methacrylic (i.e. Surlyn®) acid. In addition, two or more types of ionomeric resins may be blended into the cover compositions in order to produce the desired properties of the resulting golf balls.

Along this line, the properties of the cover compositions and/or the ionomeric resins utilized in the golf ball industry vary according to the type and amount of the metal cation, the molecular weight, the composition of the base resin (i.e. the nature and the relative content of the olefin, the unsaturated carboxylic acid groups, etc.), the amount of acid, the degree of neutralization and whether additional ingredients such as reinforcement agents or additives are utilized. Consequently, the properties of the ionomer resins can be controlled and varied in order to produce golf balls having different playing characteristics, such as differences in hardness, playability (i.e. spin, feel, click, etc.), durability (i.e. impact and/or cut resistance), and resilience (i.e. coefficient of restitution).

However, while there are currently more than fifty commercial grades of ionomers available from DuPont and Exxon with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups), the degree of neutralization and additive ingredients such as reinforcement agents, etc., a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the playability characteristics previously associated with the balata cover, but also the improved impact resistance and carrying distance properties produced by the ionomeric resins. Thus, an object of the present invention is to provide golf ball cover compositions which, when utilized in golf ball construction, produce balls exhibiting improved travel distance while maintaining satisfactory playability and durability properties such as coefficient of restitution (C.O.R.).

A golf ball's coefficient of restitution (C.O.R.) is the ratio of the relative velocity of the ball after direct impact to that before impact. One way to measure the coefficient of restitution is to propel a ball at a given speed against a hard massive surface, and measure its incoming velocity and outgoing velocity. The coefficient of restitution is defined as the ratio of the outgoing velocity to incoming velocity of a rebounding ball and is expressed as a decimal. As a result, the coefficient of restitution can vary from zero to one, with one being equivalent to an elastic collision and zero being equivalent to an inelastic collision.

The coefficient of restitution of a one-piece golf ball is a function of the ball's composition. In a two-piece or a multi-layered golf ball, the coefficient of restitution is a function of the core, the cover and any additional layer. While there are no United States Golf Association (U.S.G.A.) limitations on the coefficient of restitution values of a golf ball, the U.S.G.A. requires that the golf ball cannot exceed an initial velocity of 255 feet/second. As a result, golf ball manufacturers generally seek to maximize the coefficient of restitution of a ball without violating the velocity limitation.

In various attempts to produce a high coefficient of restitution golf ball exhibiting the enhanced travel distance desired, the golfing industry has blended various ionomeric resins. However, many of these blends do not exhibit the durability and playability characteristics necessary for repetitive play and/or the enhanced travel distance desired.

It is, therefore, desirable to develop golf ball cover compositions which produce golf balls exhibiting properties of desired carrying distance (i.e., possess desirable coefficient of restitution values) over known ionomeric cover blends such as those set forth in U.S. Pat. Nos. 4,884,814 and 4,911,451, without sacrificing or improving playability and/or durability characteristics.

Furthermore, while as stated above, Surlyn® and Escor® (i.e. "Iotek") are materials of choice for golf ball cover construction when balata is not used, these materials are relatively costly. It has, therefore, become desirable to develop a low cost alternative to Surlyn® and Iotek (Escor®) ionomeric resins in golf ball cover construction while at the same time maintaining properties such as good coefficient of restitution (C.O.R.), softness, as well as the durability required for repetitive play.

These and other objects and features of the invention will be apparent from the following description and from the claims.

SUMMARY OF THE INVENTION

The present invention is directed to golf ball covers, and more particularly to golf ball cover compositions which comprise blends of high or low acid copolymers with ethylene alkyl acrylates. The golf ball covers of the invention provide a desirable low cost alternative to the Surlyn® and Iotek ionomeric resins so frequently used in golf ball cover construction when balata is not used.

The present invention is particularly directed to golf ball cover compositions which are prepared by blending an acid copolymer which contains about 1% to about 25% acrylic acid, such as an ethylene acrylic acid (EAA) copolymer, with an ethylene copolymer including up to about 30% by weight of an alkyl acrylate. The alkyl acrylate in the ethylene copolymer may be selected from among ethyl acrylate, methyl acrylate, butyl acrylate, or others. The ethylene copolymer may, therefore, comprise among others ethylene ethyl acrylate (EEA), ethylene methyl acrylate (EMA), and/or ethylene butyl acrylate (EBA). The blending step is followed by the addition of a cation or cation blend for neutralization.

The selection of type and ratio of the ethylene acrylic acid (EAA) copolymer to the ethylene alkyl acrylate (i.e., EEA, EBA, EMA, etc.) is based on the desired final hardness and spin rate of the ball. Preferably, the blend of the acid copolymer with the non-acid functional ethylene alkyl acrylate includes about 30 to 90 parts by weight acid copolymer, and about 10 to 70 parts by weight ethylene alkyl acrylate. More preferably, the blend is comprised of about 40 to 50 parts by weight acid copolymer and about 50 to 60 parts by weight ethylene alkyl acrylate. Most preferably the blend consists of about 50 to about 70 parts by weight acid copolymer and about 30 to 50 parts by weight ethylene alkyl acrylate.

In another aspect, the invention relates to a metal cation neutralized ionomer resin comprising a blend of i) a copolymer of about 1 weight percent to about 25 weight percent, preferably greater than 16 weight percent of an alpha, beta-unsaturated carboxylic acid (preferably acrylic acid) and an olefin (preferably ethylene), and ii) an ethylene alkyl acrylate. Approximately, 10% to about 90% of the carboxyl groups of the acid copolymer are neutralized with a metal cation such as a metal cation selected from the group consisting of manganese, lithium, potassium, calcium, maganese, zinc, sodium, and nickel.

In a further aspect, the present invention concerns a metal cation neutralized high acid ionomer resin comprising a blend of i) a copolymer consisting of about 17 to 25 percent by weight acrylic acid with the remainder, or balance, thereof being ethylene and ii) an ethylene alkyl acrylate. Approximately, 10% to 90% of the carboxyl groups of the acid copolymer are neutralized with a metal cation such as a metal cation selected from the group consisting of manganese, lithium, potassium, zinc, sodium, magnesium, calcium, and nickel.

In another further aspect, the invention relates to a golf ball comprising a core and a cover, wherein the cover is comprised of a blend of i) a copolymer of about 20% by weight of an acrylic acid and the remainder ethylene and ii) an ethylene alkyl acrylate, of which 10% to 90% of the carboxyl groups of the acrylic acid/ethylene copolymer are neutralized with a metal cation such as a metal cation selected from the group consisting of manganese, lithium, potassium, sodium, zinc, magnesium, calcium and nickel. In addition, the cover may contain one or more additional ingredients such as pigments, dyes, U.V. absorbers and optical brighteners. The core is generally a solid core.

Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the development of golf ball covers, and more particularly to golf ball cover compositions which comprise blends of ethylene copolymers (i.e., ethylene alkyl acrylates) with acid copolymers. These blends may be reacted with a neutralizing compound such as magnesium oxide, zinc oxide, zinc acetate, etc. In this regard, a golf ball cover having good durability, playability (spin) and C.O.R. at a low cost relative to Surlyn® or Iotek is provided.

The acid copolymer used herein may contain anywhere from 1 to 25 percent by weight and, it is preferable to utilize a high acid copolymer (i.e. a copolymer containing greater than 16% by weight acid, preferably from about 17 to about 25 weight percent acid, and more preferably about 20 weight percent acid). The acid copolymer is blended with the ethylene alkyl acrylate and the blend is neutralized with a metal cation salt capable of ionizing or neutralizing the copolymer to the extent desired (i.e. from about 10% to 90%).

The base acid copolymer is preferably made up of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid and an alpha-olefin. Optionally, a softening comonomer can be included in the copolymer. Generally, the alpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene, and the unsaturated carboxylic acid is a carboxylic acid having from about 3 to 8 carbons. Examples of such acids include acrylic acid, methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, with acrylic acid being preferred.

The softening comonomer that can be optionally included in the invention may be selected from the group consisting of vinyl esters of aliphatic carboxylic acids wherein the acids have 2 to 10 carbon atoms and vinyl ethers wherein the alkyl groups contain 1 to 10 carbon atoms.

Consequently, examples of a number of copolymers suitable for use in the invention include, but are not limited to, high acid embodiments of an ethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer, an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer, an ethylene/methacrylic acid/vinyl acetate copolymer, an ethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymer broadly contains greater than 16% by weight unsaturated carboxylic acid, from about 30 to about 83% by weight ethylene and from 0 to about 40% by weight of a softening comonomer. More preferably, the copolymer contains about 20% by weight unsaturated carboxylic acid and about 80% by weight ethylene. Most preferably, the copolymer contains about acrylic acid with the remainder being ethylene.

Along these lines, examples of the preferred high acid base copolymers which fulfill the criteria set forth above, are a series of ethylene-acrylic acid copolymers which are commercially available from The Dow Chemical Company, Midland, Mich., under the "Primacor" designation. These high acid base copolymers exhibit the typical properties set forth below in Table 1.

                                      TABLE 1                                      __________________________________________________________________________     Typical Properties of Primacor                                                 Ethylene-Acrylic Acid Copolymers                                                                MELT TENSILE                                                                              FLEXURAL                                                                              VICAT                                            PERCENT                                                                              DENSITY,                                                                             INDEX,                                                                              YD. ST                                                                               MODULUS                                                                               SOFT PT                                                                              SHORE D                               GRADE                                                                               ACID  glcc  g/10 min                                                                            (psi) (psi)  (°C.)                                                                         HARDNESS                              __________________________________________________________________________     ASTM       D-792 D-1238                                                                              D-638 D-790  D-1525                                                                               D-2240                                5980 20.0  0.958  300.0                                                                              --    4800   43    50                                    5990 20.0  0.955 1300.0                                                                              650   2600   40    42                                    5990 20.0  0.955 1300.0                                                                              650   3200   40    42                                    5981 20.0  0.960  300.0                                                                              900   3200   46    48                                    5983 20.0  0.958  500.0                                                                              850   3100   44    45                                    5991 20.0  0.953 2600.0                                                                              635   2600   38    40                                    __________________________________________________________________________      .sup.1 The Melt Index values are obtained according to ASTM D1238, at          190° C.                                                           

Due to the high molecular weight of the Primacor 5981 grade of the ethylene-acrylic acid copolymer, this copolymer is the more preferred grade utilized in the invention.

Other acid copolymers which may be used include an ethylene-methacrylic acid copolymer such as Nucrel® available from E.I. DuPont de Nemours & Co. Nucrel® is an ethylene copolymer which is inherently flexible like EVA copolymers, and which offers desirable performance characteristics similar to those of Surlyn® ionomers.

The Nucrel® acid copolymers are produced by reacting ethylene and methacrylic acid in the presence of free radical initiators. A branched, random ethylene methacrylic acid (EMAA) copolymer is produced thereby. Carboxyl groups are distributed along the chain and interact with carboxyl groups on adjacent molecules to form a weakly crosslinked network through hydrogen bonding. The carboxyl groups disrupt the linearity of the polyethylene.

Nucrel® ethylene copolymers offer tensile strength as high as 25 MPa (3,600 psi) and good performance at low temperatures (945 k J/m² at -40° C). Properties of selected Nucrel® ethylene copolymers are listed in Table 2.

    TABLE 2       - TYPICAL PROPERTIES OF NUCREL ®       ETHYLENE COPOLYMER RESINS              NUCREL ® NUCREL ® NUCREL      ® NUCREL ® NUCREL ® NUCREL ® NUCREL ® NUCREL ®      NUCREL ® NUCREL       ®                                                 PROPERTY UNITS      ASTM 010 035 403 410 535 599 699 714 925 960       Melt Index dg/min D1238 11 35 3.0 10 35 500 88 14 21 60       Density g/cm.sup.3 D792 .934 0.94 .934 .933 .934 .918 .937 .937 0.97      .941       Tensile MPa (kpsi) D638 22.1 17.9 24.7 21.4 21.4 10.3 15.2 22.7 25 21.4       Strength   (3.2) (2.6) (3.6) (3.1) (3.1) (1.5) (2.2) (3.3) (3.6) (3.1)        Elongation % D638 630 640 568 600 580 530 560 560 520 540       Flexural MPa (kpsi) D790       Modulus       23°       C.   40.0 59 152 93.8 71 64.8 68.3 66.9 74 55.1               (73.degree      . F.)   (5.8) (8.6) (22) (13.6) (10.3) (9.4) (9.9) (9.7) (10.8) (8.0)          Hardness Shore D D2240 40 40 53 49 48 42 46 50 50 46       Vicat °C. D1525, 64 60 83 80 75 65 71 74 67 62       Softening (°F.) Rate B (147) (140) (181) (176) (167) (149) (160)      (165) (153) (144)       Temperature       Notched Izod J/m (ft-lb/in) 256 NB.sup.1 374 (7) NB NB NB NB NB NB 801      (15) NB       Tensile kJ/m.sup.2 (ft-lb/in.sup.2) 1822S       Impact       23°       C.   998 1,060 756 872 723 413 491 812 755 606                2(73.degre      e. F.)   (475) (505) (360) (415) (344) (196) (233) (386) (360) (289)           -40°       C.   647 945 442 707 486 55 288 465 275 342              (-40  F.)      (308) (450) (210) (336) (231) (26) (137) (221) (130) (163)      NB.sup.1 = No Break

The cover may comprise about 30-90 percent by weight of an acid copolymer, preferably about 40-80 percent, and most preferably 50-70 percent acid copolymers. At the same time, the cover may comprise about 10-70 percent by weight of an ethylene copolymer, preferably 20-60 percent, and most preferably 30-50 percent ethylene copolymer.

Ethylene copolymers which may be used herein include ethylene-ethyl acrylate (EEA), ethylene-methyl acrylate (EMA), and ethylene-butyl acrylate copolymers. Ethylene-ethyl acrylate is made by the polymerization of ethylene units with randomly distributed ethylene acrylate (EA) comonomer groups. The ethylene-ethyl acrylate copolymers contain up to about 30% by weight of ethylene acrylate. They are tough, flexible products having a relatively high molecular weight. They have good flexural fatigue and low temperature properties (down to -65° C.). In addition, EEA resists environmental stress cracking as well as ultraviolet radiation.

Examples of ethylene-ethyl acrylate which may be used herein include Bakelite® DPD-6169 or Bakelite® DPD-6182 available from Union Carbide. Properties of these and other suitable ethylene-ethyl acrylate copolymers include:

                  TABLE 3                                                          ______________________________________                                         TYPICAL PROPERTIES OF UNION CARBIDE                                            ETHYLENE-ETHYL ACRYLATE                                                                       TEST      DPD-    DPD-  DPD-                                    PROPERTY       METHOD    6169    6182  9169                                    ______________________________________                                         Melt Index, g/10 minutes                                                                      D 1238    6       1.5   20                                      Density, g/cm.sup.3                                                                           D 1505    0.931   0.930 0.931                                   Flexural Modulus, psi.sup.(a)                                                                 D 790     9,500   13,000                                                                               9,000                                   Secant Modulus of                                                                             D 638     5,000   6,200 4,300                                   Elasticity, psi.sup.(a)                                                        Ultimate Elongation, %.sup.(a)                                                                D 638     700     700   750                                     Tensile Strength, psi.sup.(a)                                                                 D 638     1,600   2,100 700                                     Yield Strength, psi.sup.(b)                                                                   D 638     550     700                                           Bent Strip Stress Cracking                                                                    D 1693    >500    <1,000                                                                               350                                     Resistance, 100% "Igepal"                                                      Solvent, F.sub.50, hours                                                       Durometer Hardness,                                                                           D 676                                                           "A"                      88      87    86                                      "D"                      32      32    31                                      Brittleness Index, 50%                                                                        D 746     -105    66                                            Failure, °C.                                                            Vicat Softening Point, °C.                                                             D 1525    64                                                    Compression Set, 10 days                                                                      D 395     56                                                    at 23° C., % recovery                                                   ______________________________________                                          .sup.(a) Determined on 0.075 inch compression molded plaques.                  .sup.(b) Determined on 0.075 inch compression molded plaques. Material ha      no true yield point. Value represents tensile strength at 50% elongation.

EEA is similar to ethylene vinyl acetate (EVA) in its density-property relationships and high-temperature resistance. In addition, like EVA, EEA is not resistant to aliphatic and aromatic hydrocarbons. For comparison purposes, some typical properties of ionomers as well as ethylene vinyl acetate and ethylene ethyl acrylate are provided below:

                  TABLE 4                                                          ______________________________________                                         TYPICAL PROPERTIES OF IONOMERS AND EEA                                                    Ionomer                                                                               EVA      EEA     UNITS                                       ______________________________________                                         Specific gravity                                                                            0.93     0.93-0.95                                                                               0.93                                            Yield strength                                                                              2.2      1.3      1.05  10.sup.3 lbf/in.sup.2                     Tensil modules                                                                              28-40    11       6     10.sup.3 lbf/in.sup.2                     Usual form of fracture                                                                      tough    tough    tough                                           Vicat softening point                                                                       71       83       64    °C.                                ASTM brittleness                                                                            -100     -70      -100  °C.                                temperature                                                                    Power Factor 10.sup.2 Hz                                                                    0.0015   0.0024   0.001                                           Dielectric constant                                                                         2.5      2.8      2.8                                             10.sup.3 Hz                                                                    ______________________________________                                    

Ethylene-methyl acrylate copolymers contain up to about 30% by weight of methyl acrylate and yield blown films having rubberlike limpness and high impact strength. These copolymers may be useful in coating and laminating applications as a result of their good adhesion to commonly used substrates. EMAs have good heat-seal characteristics.

Ethylene-methyl acrylate copolymers are manufactured by reacting, at high temperatures and pressures, methyl-acrylate monomers with ethylene and free radical initiators. Polymerization occurs such that the methyl acrylate forms random side chains on the polyethylene backbone. The acrylic functionality decreases resin crystallinity and increases polarity to enhance resin properties. The properties depend on molecular weight (determined by melt index) and percent crystallinity. Percent crystallinity is determined by comonomer incorporation. As the comonomer content increases, the film become softer, tougher, and easier to heat seal.

EMA films have low modulus (<10,000 psi), low melting points, and good impact strength. In addition, the EMA resins are highly polar, and as a result are compatible with olefinic and other polymers. They adhere well to many substrates including LDPE, LLDPE, and EVA.

Examples of ethylene-methyl acrylate which may be used in the golf ball cover compositions of the present invention include the Optema™ or Escor® EMA copolymer resins available from Exxon Chemical Company. The Optema™/Escor® EMA resins are thermally stable ethylene methyl acrylate resins which will accept up to 65% or more fillers and pigments without losing their properties. They are more thermally stable than EVAs and can be extruded or molded over a range of 275°-625° F. (compared to an EVA limit of 450° F.). EMAs are generally not corrosive when compared to EVAs, EAAs and ionomers. Some of the typical properties associated with the various grades of Optema™ EMA resins are found in the following Table 5:

    TABLE 5       - PROPERTIES OF OPTEMA ™       EMA RESINS                                            VICAT          TENSILE FLEXURAL   TENSILE  SOFTENING       MELT INDEX   STRENGTH MODULUS  HARDNESS IMPACT       ®  PT                 dg/min METHYL DENSITY psi (MPa) psi (MPa)      MELTIN SHORE A/D 73° F. (23° C.) ELONGATION (10,000)             (ASTM ACRYLATE g/cm.sup.3 (ASTM (ASTM (ASTM POINT (ASTM (ASTM %      (ASTM (ASTM       D1238) WT % D1505) D638) D790) °F. (°C.) D2240) D1822)      D638) D1525)       OPTEMA       GRADE       TC 020 6.0 6.5 0.928 1700 (12) 17500 (120) 215 (102) >90/45  170 (360)      >800 172 (78)       TC 115 0.7 16.5 0.938 1900 (13) 8300 (57) 185 (85) 91/41 260 (550) >800      149 (65)       TC 114 3.2 18.0 0.948 1700 (12) 7100 (49) 178 (81) 89/38 260 (570) >800      133 (56)       TC 110 2.0 21.5 0.942 1600 (11) 5100 (35) 167 (75) 86/36 270 (570) >800      126 (52)       TC 111 2.0 21.5 0.944 1600 (11) 5100 (35) 167 (75) 86/36 270 (570) >800      126 (52)       TC 120 6.0 20. 0.942 1600 (11) 5100 (35) 169 (76) 86/35 250 (520) >800      117 (47)       TC 130 20.0 21.5 0.941 1300 (9) 4900 (34) 167 (75) 85/33 230 (480) >800      109 (43)       TC 140 135.0 21.5 0.939 1200 (8) 4900 (34) 162 (72) 84/32 170 (360)      >800 97 (36)       TC 113 1.0 23.5 0.939 1600 (11) 3700 (26) 165 (74) 83/33 310 (650) >800      122 (50)       TC 220 5.0 24.0 0.945 1300 (9) 3900 (27) 156 (69) 82/32 280 (580) >800      109 (43)       TC 221 5.0 27.0 0.948 1100 (8) 2800 (19) 147 (64) 79/28 280 (590) >800      102 (39)       DEVELOPMENTAL       GRADES       XS-11.04 6.0 6.0 0.933 1410 (13.3) 11,4000 (78.6) 225 (107) 90/35 170      (363) 1450 182 (84)       XS-12.04 3.0 28.0 0.953 760 (5.0) 1210 (8.3) 145 (63) 70/17 -- 1060 --        XS-13.04 135.0 20. 0.940 700 (4.8) 2800 (19) 171 (77) 82/25 -- 1400      121 (50)

Certain developmental grades of Optema™ EMAs may be used in formulating the golf ball covers herein. These developmental grades of resins are designated "XS". Pertinent properties of XS-11.04, 12.04 and 13.04 are set forth above in Table 5. Melt index and methyl acrylate content of these and certain others are set forth in the following Table 6:

                  TABLE 6                                                          ______________________________________                                         PROPERTIES OF OPTEMA ® DEVELOPMENTAL                                       EMA RESINS                                                                                  MELT INDEX  METHYLACRYLATE                                        OPTEMA/GRADE (dg/min)    CONTENT (%)                                           ______________________________________                                         XS-53.04     0.7         15                                                    XS-54.04     1.0         24                                                     XS-34.14*   2.0         20                                                    XS-12.04     3.0         28                                                    XS-61.48     5.0         24                                                    XS-55.48     5.0         28                                                    XS-11.04     6.0         6                                                     XS-13.04     135.0       20                                                    ______________________________________                                          *Slip and antiblock added.                                               

Chevron Chemical Company's ethylene-butyl acrylate copolymer, EBAC™, is stable at high temperatures, and may be processed as high as 600° F. Typical properties (or average values) of certain EBAC™ copolymers are set forth below in Table 7.

                                      TABLE 7                                      __________________________________________________________________________     PROPERTIES OF ETHYLENE-BUTYL ACRYLATE COPOLYMERS (EBAC ™)                                    EBAC ™                                                                            EBAC ™                                                                            EBAC ™                                                                            EBAC ™                                                                            EBAC ™                                              DS-   DS-   DS-   DS-   DS-                                   PROPERTIES                                                                             UNITS                                                                               ASTM                                                                               1263-70                                                                              1120-70                                                                              1122-70                                                                              1123-70                                                                              1256-70                               __________________________________________________________________________     Melt Flow                                                                              gms/10                                                                              D-1238                                                                             0.5   2.0   6.0   20    3.0                                           min                                                                    Butyl   %    --  18    20    20    20    28.0                                  Acrylate                                                                       Content                                                                        Density gm/cc                                                                               D-1505                                                                             0.927 0.927 0.927 0.927 0.927                                 Melting °C.                                                                          --  91    90    87    88    74                                    Point                                                                          Vicat   °C.                                                                          D-1525                                                                             65    60    55    49    --                                    Softening                                                                      Point                                                                          Brittleness                                                                            °C.                                                                          D-746                                                                              <-76  <-75  <-75  <-75  <-76                                  Temperature                                                                    Hardness                                                                       Shore A --   D-2240                                                                             --    --    88    88    74                                    Shore D --   D-2240                                                                             38    33    --    27    23                                    Flexural                                                                               psi  D-747                                                                              4000  --    --    3000  --                                    Stiffness                                                                      Tensile psi  D-638                                                                              2000  1400  1100  680   760                                   Ultimate.sup.2                                                                 Tesnile @                                                                              psi  D-638                                                                              1900  1400  1100  680   760                                   Break.sup.2                                                                    Elongation                                                                             %    D-638                                                                              810   900   850   620   950                                   @ Point                                                                        Break.sup.2                                                                    __________________________________________________________________________      .sup.1 Melt Flow testing of condition E, 190° C. and 2.16 kg            weight.                                                                        .sup.2 Tensile Properties determined with Type IV compression molded           samples, 20"/min crosshead speed.                                        

The metal cation salts utilized in the invention are those salts which provide the metal cations capable of neutralizing, to various extents, the carboxylic acid groups of the high acid copolymer. These include acetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium, potassium, nickel, magnesium, and manganese.

Examples of such lithium ion sources are lithium hydroxide monohydrate, lithium hydroxide, lithium oxide and lithium acetate. Sources for the calcium ion include calcium hydroxide, calcium acetate and calcium oxide. Suitable zinc ion sources are zinc acetate dihydrate and zinc acetate, a blend of zinc oxide and acetic acid. Examples of sodium ion sources are sodium hydroxide and sodium acetate. Sources for the potassium ion include potassium hydroxide and potassium acetate. Suitable nickel ion sources are nickel acetate, nickel oxide and nickel hydroxide. Sources of magnesium include magnesium oxide, magnesium hydroxide, magnesium acetate. Sources of manganese include manganese acetate and manganese oxide.

The cover compositions of the invention are produced by reacting the blend of the acid copolymer and the ethylene alkyl acrylate with various amounts of the metal cation salts above the crystalline melting point of the copolymer, such as at a temperature from about 200° F. to about 500° F., preferably from about 250° F. to about 350° F. under high shear conditions at a pressure of from about 100 psi to 10,000 psi. Other well known blending techniques may also be used. The amount of metal cation salt utilized to produce the cover compositions is the quantity which provides a sufficient amount of the metal cations to neutralize the desired percentage of the carboxylic acid groups in the high acid copolymer. The extent of neutralization is generally from about 10% to about 90%.

Additional compatible additive materials may also be added to the compositions of the present invention, such as dyes (for example, Ultramarine Blue sold by Whitaker, Clark, and Daniels of South Painsfield, N.J.), and pigments, i.e. white pigments such as titanium dioxide (for example Unitane 0-110) zinc oxide, and zinc sulfate, as well as fluorescent pigments. As indicated in U.S. Pat. No. 4,884,814, the amount of pigment and/or dye used in conjunction with the polymeric cover composition depends on the particular base ionomer mixture utilized and the particular pigment and/or dye utilized. The concentration of the pigment in the polymeric cover composition can be from about 1% to about 10% as based on the weight of the base ionomer mixture. A more preferred range is from about 1% to about 5% as based on the weight of the base ionomer mixture. The most preferred range is from about 1% to about 3% as based on the weight of the base ionomer mixture. The most preferred pigment for use in accordance with this invention is titanium dioxide.

Moreover, since these are various hues of white, i.e. blue white, yellow white, etc., trace amounts of blue pigment may be added to the cover stock composition to impart a blue white appearance thereto. However, if different hues of the color white are desired, different pigments can be added to the cover composition at the amounts necessary to produce the color desired.

In addition, it is within the purview of this invention to add to the cover compositions of this invention compatible materials which do not affect the basic novel characteristics of the composition of this invention. Among such materials are antioxidants (i.e. Santonox R), antistatic agents, stabilizers and processing aids. The cover compositions of the present invention may also contain softening agents, such as plasticizers, etc., and reinforcing materials such as glass fibers and inorganic fillers, as long as the desired properties produced by the golf ball covers of the invention are not impaired.

Furthermore, optical brighteners, such as those disclosed in U.S. Pat. No. 4,679,795, may also be included in the cover composition of the invention. Examples of suitable optical brighteners which can be used in accordance with this invention are Unitex OB as sold by the Ciba-Geigy Chemical Company, Ardaley, N.Y. Unitex OB is thought to be 2, 5-Bis (5-tert-butyl-2-benzoxazoly) thiophene. Examples of other optical brighteners suitable for use in accordance with this invention are as follows: Leucopure EGM as sold by Sandoz, East Hanover, N.J. 07936. Leucopure EGM is thought to be 7-(2h-naphthol (1,2-d)-triazol-2yl)-3phenyl-coumarin. Phorwhite K-20G2 is sold by Mobay Chemical Corporation, P.O. Box 385, Union Metro Park, Union, N.J. 07083, and is thought to be a pyrazoline derivative, Eastobrite OB-1 as sold by Eastman Chemical Products, Inc. Kingsport, Tenn., is thought to be 4,4-Bis (- benzoxaczoly) stilbene. The above-mentioned Uvitex and Eastobrite OB-1 are preferred optical brighteners for use in accordance with this invention.

Moreover, since many optical brighteners are colored, the percentage of optical brighteners utilized must not be excessive in order to prevent the optical brightener from functioning as a pigment or dye in its own right.

The percentage of optical brighteners which can be used in accordance with this invention is from about 0.01% to about 0.5% as based on the weight of the polymer used as a cover stock. A more preferred range is from about 0.05% to about 0.25% with the most preferred range from about 0.10% to about 0.020% depending on the optical properties of the particular optical brightener used and the polymeric environment in which it is a part.

Generally, the additives are admixed with a ionomer to be used in the cover composition to provide a masterbatch (M.B.) of desired concentration and an amount of the masterbatch sufficient to provide the desired amounts of additive is then admixed with the copolymer blends.

The cover compositions of the present invention may be produced according to conventional melt blending procedures. In this regard, the above indicated high acid ionomeric resins are blended along with the masterbatch containing the desired additives in a Banbury type mixer, two-roll mill, or extruded prior to molding. The blended composition is then formed into slabs or pellets, etc. and maintained in such a state until molding is desired. Alternatively a simple dry blend of the pelletized or granulated resins and color masterbatch may be prepared and fed directly into the injection molding machine where homogenization occurs in the mixing section of the barrel prior to injection into the mold. If necessary, further additives such as an inorganic filler, etc., may be added and uniformly mixed before initiation of the molding process.

Moreover, golf balls of the present invention can be produced by molding processes currently well known in the golf ball art. Specifically, the golf balls can be produced by injection molding or compression molding the novel cover compositions about wound or solid molded cores to produce a golf ball having a diameter of about 1.680 inches or greater and weighing about 1.620 ounces. The standards for both the diameter and weight of the balls are established by the United States Golf Association (U.S.G.A.). Although both solid core and wound cores can be utilized in the present invention, as a result of their lower cost and superior performance, solid molded cores are preferred over wound cores.

Conventional solid cores are typically compression molded from a slug of uncured or lightly cured elastomer composition comprising a high cis content polybutadiene and a metal salt of an α, β, ethylenically unsaturated carboxylic acid such as zinc mono or diacrylate or methacrylate. To achieve higher coefficients of restitution in the core, the manufacturer may include a small amount of a metal oxide such as zinc oxide. In addition, larger amounts of metal oxide than those that are needed to achieve the desired coefficient may be included in order to increase the core weight so that the finished ball more closely approaches the U.S.G.A. upper weight limit of 1.620 ounces. Other materials may be used in the core composition including compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiator catalysts such as peroxides are admixed with the core composition so that on the application of heat and pressure, a complex curing or cross-linking reaction takes place.

The term "solid cores" as used herein refers not only to one piece cores but also to those cores having a separate solid layer beneath the cover and above the core as in U.S. Pat. No. 4,431,193, and other multilayer and/or non-wound cores (such as those described in U.S. Pat. No. 4,848,770).

Wound cores are generally produced by winding a very large elastic thread around a solid or liquid filled balloon center. The elastic thread is wound around the center to produce a finished core of about 1.4 to 1.6 inches in diameter, generally. Since the core material is not an integral part of the present invention, a detailed discussion concerning the specific types of core materials which may be utilized with the cover compositions of the invention are not specifically set forth herein. In this regard, the cover compositions of the invention may be used in conjunction with any standard golf ball core.

As indicated, the golf balls of the present invention may be produced by forming covers consisting of the compositions of the invention around cores by conventional molding processes. For example, in compression molding, the cover composition is formed via injection at about 380° F. to about 450° F. into smooth surfaced hemispherical shells which are then positioned around the core in a dimpled golf ball mold and subjected to compression molding at 200°-300° F. for 2-10 minutes, followed by cooling at 50°-70° F. for 2-10 minutes, to fuse the shells together to form an unitary ball. In addition, the golf balls may be produced by injection molding, wherein the cover composition is injected directly around the core placed in the center of a golf ball mold for a period of time at a mold temperature of from 50° F. to about 100° F. After molding the golf balls produced may undergo various further finishing steps such as buffing, painting, and marking as disclosed in U.S. Pat. No. 4,911,451.

The present invention is further illustrated by the following examples in which the parts of the specific ingredients are by weight (pbw). It is to be understood that the present invention is not limited to the examples, and various changes and modifications may be made in the invention without departing from the spirit and scope thereof.

EXAMPLES

By blending the ingredients set forth in the Tables below, a series of golf ball cover formulations were produced. Finished golf balls were prepared using the cover compositions of the present invention, controls and comparative cover compositions by positioning a solid preformed cross-linked polybutadiene core in an injection molding cavity in such a manner to permit the uniform injection of the selected cover composition over each core. Along this line, the cover formulations were injection molded at about 400° F. around identical solid type cores having a finished diameter of 1.545 inches to produce golf balls approximately 1.680 inches in diameter having a normal cover thickness of 0.0675 inches. All materials were molded under essentially identical conditions. The properties of coefficient of restitution (C.O.R.) of the molded and finished balls, Shore D hardness, cold crack resistance, spin rates, etc. for the cover compositions were then determined.

In conducting the comparative prior art testing, Escor® 4000/7030 and Escor® 900/8000 ionomers were utilized. In this regard, blends of Escor® 4000/7030 and Escor® 900/8000 (i.e. the subject of U.S. Pat. No. 4,911,451) are considered by the inventors to be generally among the best prior art cover compositions concerning ethylene-acrylic acid ionomer (low acid) blends.

The data for each example represents the average data for one dozen balls produced according to the desired manner. The properties for the Examples were measured according to the following parameters:

Coefficient of restitution (C.O.R.) was measured by firing the resulting golf ball in an air cannon at a velocity of 125 feet per second against a steel plate which is positioned 12 feet from the muzzle of the cannon. The rebound velocity was then measured. The rebound velocity was divided by the forward velocity to give the coefficient of restitution.

Shore hardness was measured in accordance with ASTM Test D-2240.

Cold cracking resistance was measured by firing balls from an air cannon, 5 blows at 165 feet/sec, after the balls had been conditioned for 24 hours at -10° F. After allowing the balls to equilibrate to room temperature the balls are inspected for cover cracking.

The spin rate of the golf ball was measured by striking the resulting golf balls with a pitching wedge or 9-iron wherein the club-head speed is about 80 feet per second and the ball is launched at an angle of 26 to 34 degrees with an initial velocity of about 110-115 feet per second. The spin rate was measured by observing the rotation of the ball in flight using stop action Strobe photography.

EXAMPLE 1 Preparation of Acrylic Acid Based High Acid Ionomers

A number of new cation neutralized acrylic acid based high acid ionomer resins were prepared utilizing as the copolymer of an olefin and an alpha, beta-unsaturated carboxylic acid, a 20 weight percent acrylic acid/ethylene copolymer produced by The Dow Chemical Company, Midland, Mich. under the designation "Primacor 5981." According to The Dow Chemical Company, Primacor 5981 has a melt index (at 190° C., 2150 g) of 300 g/10 min. The carboxylic acid groups present in the 20 weight percent acrylic acid/ethylene copolymer were neutralized to various weight percentages by a number of different metal cation salts resulting in the production of several new thermoplastic elastomers exhibiting enhanced properties for golf ball cover production. Due to differences in the nature of the cation salts, the amount of cation salts utilized, etc., the new high acid ionomer resins produced differed substantially in the extent of neutralization and in melt indices, as well as in resilience (i.e. C.O.R.) and hardness values.

For the purpose of determining the weight percent of neutralization of the carboxylic acid groups in the acrylic acid/ethylene copolymer after reacting with various cation salts, it was assumed that 1 mole of sodium (Na⁺), potassium (K⁺), and lithium (Li⁺) neutralized one mole of acrylic acid, and that one mole of zinc (Zn²⁺), magnesium (Mg²⁺), manganese (Mn²⁺), calcium (Ca²⁺) and nickel (Ni²⁺) neutralized two moles of acrylic acid. The calculations of neutralization were based upon an acrylic acid molecular weight of 79 g/m, giving 0.2778 moles per 100 grams of copolymer.

As indicated below in Table 8, the various cation salts were added in variable amounts to the 20 weight percent acrylic acid/ethylene copolymer in order to determine the optimal level of neutralization for each of the cations. In Table 8, NaOH refers to sodium hydroxide (formula weight of 40). MnAc refers to manganese acetate tetrahydrate having a formula weight of 245. LiOH is lithium hydroxide, fwt=24. KOH is potassium hydroxide, fwt=56. ZnAc is zinc acetate dihydrate, fwt=219.5. MgAc is magnesium acetate tetrahydrate, fwt=214.4. CaAc is calcium acetate, fwt=158. MgO is magnesium oxide, fwt=40.3. NiAc is nickel acetate, fwt=176.8. All of these cation salts are solids at room temperature.

The specific cation salts were added in differing amounts with the 20 weight percent acrylic acid/ethylene copolymer (i.e. the Primacor 5981) to an internal mixer (Banbury type) for the neutralization reaction. The only exception was calcium acetate, which, due to problems encountered in solid form, was added as a 30 wt-% solution in water.

In the neutralization reaction, the cation salts solubilized in the Primacor 5981 acrylic acid/ethylene copolymer above the melting point of the copolymer and a vigorous reaction took place with a great deal of foaming occurring as the cation reacted with the carboxylic acid groups of the acrylic acid/ethylene copolymer and the volatile by-products of water (in the case of oxides or hydroxides) or acetic acid (when acetates are used) were evaporated. The reaction was continued until foaming ceased (i.e. about 30-45 minutes at 250°-350° F.), and the batch was removed from the Banbury mixer. Mixing continued of the batch obtained from the mixer on a hot two-roll mill (175°-250° F.) to complete the neutralization reaction. The extent of the reaction was monitored by measuring melt flow index according to ASTM D-1238-E. As indicated below, the neutralized products exhibited drastically different properties depending upon the nature and amount of the cation salts utilized.

                                      TABLE 8                                      __________________________________________________________________________              Wt-%  Wt-%    Melt     Shore D                                        Formulation No.                                                                         Cation Salt                                                                          Neutralization                                                                         Index                                                                               C.O.R.                                                                             Hardness                                       __________________________________________________________________________     1(NaOH)  6.98  67.5    0.9  .804                                                                               71                                             2(NaOH)  5.66  54.0    2.4  .808                                                                               73                                             3(NaOH)  3.84  35.9    12.2 .812                                                                               69                                             4(NaOH)  2.91  27.0    17.5 .812                                                                               (brittle)                                      5(MnAc)  19.6  71.7    7.5  .809                                                                               73                                             6(MnAc)  23.1  88.3    3.5  .814                                                                               77                                             7(MnAc)  15.3  53.0    7.5  .810                                                                               72                                             8(MnAc)  26.5  106     0.7  .813                                                                               (brittle)                                      9(LiOH)  4.54  71.3    0.6  .810                                                                               74                                             10(LiOH) 3.38  52.5    4.2  .818                                                                               72                                             11(LiOH) 2.34  35.9    18.6 .815                                                                               72                                             12(KOH)  5.30  36.0    19.3 Broke                                                                              70                                             13(KOH)  8.26  57.9    7.18 .804                                                                               70                                             14(KOH)  10.7  77.0    4.3  .801                                                                               67                                             15(ZnAc) 17.9  71.5    0.2  .806                                                                               71                                             16(ZnAc) 13.9  53.0    0.9  .797                                                                               69                                             17(ZnAc) 9.91  36.1    3.4  .793                                                                               67                                             18(MgAc) 17.4  70.7    2.8  .814                                                                               74                                             19(MgAc) 20.6  87.1    1.5  .815                                                                               76                                             20(MgAc) 13.8  53.8    4.1  .814                                                                               74                                             21(CaAc) 13.2  69.2    1.1  .813                                                                               74                                             22(CaAc) 7.12  34.9    10.1 .808                                                                               70                                             __________________________________________________________________________       Controls:                                                                     50/50 Blend of Ioteks 8000/7030 C.O.R. = .810/65 Shore D Hardness              DuPont High Acid Surlyn ® 8422 (Na) C.O.R. = .811/70 Shore D Hardness      DuPont High acid Surlyn ® 8162 (Zn) C.O.R. = .807/65 Shore D Hardness      Exxon High Acid Iotek EX960 (Zn) C.O.R. = .796/65 Shore D Hardness       

             Wt-%  Wt-%    Melt                                                    Formulation No.                                                                         Cation Salt                                                                          Neutralization                                                                         Index                                                                               C.O.R.                                             __________________________________________________________________________     23(MgO)  2.91  53.5    2.5  .813                                               24(MgO)  3.85  71.5    2.8  .808                                               25(MgO)  4.76  89.3    1.1  .809                                               26(MgO)  1.96  35.7    7.5  .815                                               __________________________________________________________________________      Control for Formulations 23-26 is 50/50 Iotek 8000/7030,                       C.O.R. = .814, Formulation 26 C.O.R. was normalized to that control            accordingly                                                              

             Wt-%  Wt-%    Melt     Shore D                                        Formulation No.                                                                         Cation Salt                                                                          Neutralization                                                                         Index                                                                               C.O.R.                                                                             Hardness                                       __________________________________________________________________________     27(NiAc) 13.04 61.1    0.2  .802                                                                               71                                             28(NiAc) 10.71 48.9    0.5  .799                                                                               72                                             29(NiAc) 8.26  36.7    1.8  .796                                                                               69                                             30(NiAc) 5.66  24.4    7.5  .786                                                                               64                                             __________________________________________________________________________      Control for Formulation Nos. 27-30 is 50/50 Iotek 8000/7030, C.O.R. = .80                                                                               

As indicated in Table 8, a number of the new cation neutralized acrylic acid based high acid ionomer resins exhibited C.O.R. and Shore D hardness values greater than that exhibited by a 50/50 blend of the Iotek low acid acrylic acid based hard ionomer resins, such as the Iotek 8000/7030 blend utilized in the cover compositions disclosed in U.S. Pat. No. 4,911,451. Moreover, included in new acrylic acid based high acid ionomer resins were numerous cation neutralized high acid ionomer resins previously not available, such as those acrylic acid based high acid ionomer resins neutralized to various degrees by the manganese, lithium, potassium, magnesium, calcium and nickel salts. Furthermore, the new cation neutralized acrylic acid based high acid ionomers produced C.O.R. and hardness values greater than those shown by the methacrylic acid based high acid ionomer resins recently produced by DuPont (i.e. Surlyn® 8422 (Na) and Surlyn® 8162 (Zn)) and the acrylic acid based high acid resins experimentally produced by Exxon (i.e. Iotek EX-959 and Ex-960 (Zn)), collectively referred to as "the controls."

In addition, the results produced by Formulation Nos. 1 through 3 directed to the sodium ion neutralized ethylene-acrylic acid copolymers and Formulation Nos. 15 through 17 directed to the zinc ion neutralized ethylene-acrylic acid copolymers in comparison to the new Iotek high acid ethylene acrylic acid ionomers were also of interest. As indicated above, Escor® or Iotek Ex-959 is a sodium ion neutralized ethylene-acrylic acid copolymer and Escor® or Iotek Ex-960 is a zinc neutralized ethylene-acrylic acid copolymer. According to Exxon, Ioteks 959 and 960 contain from about 19.0 to about 21.0% by weight acrylic acid with approximately 30 to about 70 percent of the acid groups neutralized with sodium and zinc ions, respectfully.

Formulation No. 2 (i.e. 5.66 wt-% sodium salt, 54 wt-% neutralization, 2.4 melt index, 0.808 C.O.R. and 73 Shore D hardness) is somewhat similar to Iotek 959 and Formulation No. 16 (i.e. 13.9 wt-% zinc salt, 53 wt-% neutralization, 0.9 melt index, 0.797 C.O.R. and 69 Shore D hardness) is somewhat similar to Iotek 960.

However, not only did the new cation neutralized acrylic acid based high acid ionomers exhibit similar or better resilience (C.O.R.) at comparable or better hardness values than those exhibited by the sodium or zinc high acid Iotek ionomers, as a result of the neutralization of the acrylic acid/ethylene copolymer with several different cation salts, to a number of different neutralization percentages, a wide variety of new cation neutralized acrylic acid based high acid ionomers were produced having improved resilience and hardness values. These new cation neutralized high acid ionomer resins are particularly valuable in the field of golf ball production.

More particularly, the development of a number of separate different cation neutralized high acid ionomers besides the sodium or zinc high acid ionomers available from DuPont or Exxon, such as the new manganese, lithium, potassium, magnesium, calcium and nickel acrylic acid based high acid ionomer resins, allows for the production of a wide variety of cation neutralized high acid ionomer blends. Furthermore, since the new sodium or zinc neutralized high acid ionomers produced improved properties over those produced by the existing available sodium or zinc high acid ionomers, a number of new cover compositions can be produced having enhanced characteristics.

Along this line, several of the cation neutralized acrylic acid based high acid ionomer resins produced above which exhibited enhanced C.O.R. and Shore D hardness values were blended together and evaluated for the purpose of determining whether any synergistic effects were produced particularly with respect to enhanced C.O.R. values.

Specifically, from each group of the different cation neutralized high acid ionomer resins set forth in Table 8, the best overall ionomer (based upon C.O.R., melt index and Shore D hardness) was utilized to produce a number of blends ("diblends" and "triblends") and processed to produce the cover component of multi-layered golf balls. The "diblends" consisted of 50/50 mixtures and the "triblends" consisted of a 33.33/33.33/33.33 mixtures.

With respect to the blends set forth below, Na refers to Formulation No. 3, C.O.R. (molded/finished) of 0.812/817; Mn refers to Formulation No. 6, C.O.R. (molded/finished) of 0.814/0.814; Li refers to Formulation No. 10, C.O.R. (molded/finished) of 0.818/0.819; K refers to Formulation No. 13, C.O.R. (molded/finished) of 0.805/0.809; Zn refers to Formulation No. 16, C.O.R. (molded/finished) of 0.797/0.796; Mg refers to Formulation No. 18, C.O.R. (molded/finished) of 0.814/0.820; Ca refers to Formulation No. 21, C.O.R. (molded/finished) of 0.813/0.812; Ni refers to Formulation No. 28, C.O.R. (molded/finished) of 0.799/0.817; and 50/50 Iotek 8000/7030 refers to control of 50/50 blend of Iotek 8000/7030, C.O.R. (molded/finished) of 0.810/0.812. The C.O.R. values of the "diblends" and "triblends" were then evaluated after molding with a center stock having the following composition:

    ______________________________________                                         MATERIAL           WEIGHT (phr)                                                ______________________________________                                         BR-1220.sup.1      70.70                                                       Taktene 220.sup.2  29.30                                                       React Rite ZDA.sup.3                                                                              31.14                                                       Zinc Oxide         6.23                                                        Zinc Stearate      20.15                                                       Limestone          17.58                                                       Ground Flash (20-40 mesh)                                                                         20.15                                                       Blue Masterbatch   .012                                                        Luperco 231XL.sup.4                                                                               .89                                                         or Trigonox 29/40.sup.5                                                        Papi 94.sup.6      .50                                                         ______________________________________                                          .sup.1 BR-1220 is high cispolybutadiene from Shell Chemical Co., Houston       Texas.                                                                         .sup.2 Taktene is high cispolybutadiene from Polysar Chemical.                 .sup.3 ZDA is zinc diacrylate.                                                 .sup.4 Luperco 231XL is a peroxidefree radical initiator manufactured and      sold by Atochem, Buffalo, New York.                                            .sup.5 Trigonox 29/40 is peroxidefree radical initiator manufactured and       sold by Akzo Chemie America, Chicago, Illinois.                                .sup.6 Papi 94 is a polymeric diisocyanate available from Dow Chemical         Co., Midland, Michigan.                                                  

In addition, the molded balls were coated and finished according to the procedure mentioned above. The C.O.R. values of the finished balls were determined in order to evaluate whether any improvement in resilience was produced. Generally, it is typical to observe a 0.002 to 0.003 point pick up in C.O.R. values of the finished balls in comparison to the molded balls. The results are set forth in Tables 9A, 9B and 10 below.

                  TABLE 9A                                                         ______________________________________                                         Diblends (50/50 Blends) C.O.R.                                                 (Molded/Finished) Values                                                       Formulation No.                                                                            Blend       C.O.R. (Molded/Finished)                               ______________________________________                                         31          Na/Mn       .813/.818                                              32          Na/Li       .813/.818                                              33          Na/K        .809/.816                                              34          Na/Zn       .811/.818                                              35          Na/Mg       .813/.819                                              36          Na/Ca       .811/.819                                              37          Mn/Li       .811/.817                                              38          Mn/K        .811/.818                                              39          Mn/Zn       .807/.814                                              40          Mn/Mg       .809/.816                                              41          Mn/Ca       .809/.816                                              42          Li/K        .810/.817                                              43          Li/Zn       .813/.819                                              44          Li/Mg       .812/.820                                              45          Li/Ca       .811/.818                                              46          K/Zn        .810/.815                                              47          K/Mg        .811/.820                                              48          K/Ca        .810/.817                                              49          Zn/Mg       .807/.814                                              50          Zn/Ca       .808/.814                                              51          Mg/Ca       .801/.818                                              52          Na/Ni       .809/.815                                              53          Mn/Ni       .807/.814                                              54          Li/Ni       .809/.816                                              55          K/Ni        .809/.816                                              56          Zn/Ni       .799/.804                                              57          Mg/Ni       .805/.813                                              58          Ca/Ni       .807/.815                                              59          Iotek 959/960                                                                              .811/.818                                              60          Control     .809/NA                                                61          Control     .806/NA                                                ______________________________________                                          Controls are Formulation No. 59, a 50/50 blend of Iotek 959/960;               Formulation No. 60 a 75/25 blend of Surlyn 8162/8422; and Formulation No.      61 a 50/50 blend of Iotek 8000/7030.                                     

                                      TABLE 9B                                     __________________________________________________________________________     Synergy Values of the DiBlends                                                 Formulation                                                                           Salt                                                                              Salt                                                                              (COR)                                                                              (COR)                                                                              (COR) exp-                                                                           Final Final Final                                   No.    1  2  calc                                                                               exp (COR) calc                                                                           (COR) calc                                                                           (COR) exp                                                                            (COR) Diff.                             __________________________________________________________________________     31     Na Mn 813.0                                                                              813.0                                                                              0.0   815.5 818.0 2.5                                     32     Na Li 815.0                                                                              813.0                                                                              -2.0  818.0 818.0 0.0                                     33     Na K  808.0                                                                              809.0                                                                              1.0   813.0 816.0 3.0                                     34     Na Zn 804.5                                                                              811.0                                                                              6.5   806.5 818.0 11.5                                    35     Na Mg 813.0                                                                              813.0                                                                              0.0   818.5 819.0 0.5                                     36     Na Ca 812.5                                                                              811.0                                                                              -1.5  814.5 819.0 4.5                                     37     Mn Li 816.0                                                                              811.0                                                                              -5.0  816.5 817.0 0.5                                     38     Mn K  809.0                                                                              811.0                                                                              2.0   811.5 818.0 6.5                                     39     Mn Zn 805.5                                                                              807.0                                                                              1.5   805.0 814.0 9.0                                     40     Mn Mg 814.0                                                                              809.0                                                                              -5.0  817.0 816.0 -1.0                                    41     Mn Ca 813.5                                                                              809.0                                                                              -4.5  813.0 816.0 3.0                                     42     Li K  811.0                                                                              810.0                                                                              -1.0  814.0 817.0 3.0                                     43     Li Zn 807.5                                                                              813.0                                                                              5.5   807.5 819.0 11.5                                    44     Li Mg 816.0                                                                              812.0                                                                              -4.0  819.5 820.0 0.5                                     45     Li Ca 815.5                                                                              811.0                                                                              -4.5  815.5 818.0 2.5                                     46     K  Zn 800.5                                                                              810.0                                                                              9.5   802.5 815.0 12.5                                    47     K  Mg 809.0                                                                              811.0                                                                              2.0   814.5 820.0 5.5                                     48     K  Ca 806.0                                                                              810.0                                                                              4.0   810.5 817.0 6.5                                     49     Zn Mg 805.5                                                                              807.0                                                                              1.5   808.0 814.0 6.0                                     50     Zn Ca 805.0                                                                              808.0                                                                              3.0   804.0 814.0 10.0                                    51     Mg Ca 813.5                                                                              810.0                                                                              -3.5  816.0 818.0 2.0                                     52     Na Ni 805.5                                                                              809.0                                                                              3.5   817.0 815.0 -2.0                                    53     Mn Ni 806.5                                                                              807.0                                                                              0.5   815.5 814.0 -1.5                                    54     Li Ni 808.5                                                                              809.0                                                                              0.5   818.0 816.0 -2.0                                    55     K  Ni 801.5                                                                              809.0                                                                              7.5   813.0 816.0 3.0                                     56     Zn Ni 798.0                                                                              799.0                                                                              1.0   806.5 804.0 -2.5                                    57     Mg Ni 806.5                                                                              805.0                                                                              -1.5  818.5 813.0 -5.5                                    58     Ca Ni 806.0                                                                              807.0                                                                              1.0   814.5 815.0 0.5                                     __________________________________________________________________________

In Table 9B above, the C.O.R. synergy values are based upon the data from Table 8 of the various metal cation neutralized high acid acrylic acid based ionomer resins and the following calculations:

    ______________________________________                                         (COR) calc = coefficient calculated as weighted                                average of as-molded COR's for polymers of salts 1 and 2                       (COR) exp = experimental as-molded COR for blend                               FINAL (COR) calc = coefficient calculated as                                   weighted average of finished COR's for polymers                                of salts 1 and 2                                                               FINAL (COR) exp = experimental finished COR for                                blend                                                                          FINAL (COR) diff = difference between FINAL                                    (COR) exp and FINAL (COR) (calc)                                               ______________________________________                                    

As noted in Table 9B, positive synergy in resilience is observed for nearly all of the finished (final) blends, with substantial synergy being produced in Formulation Nos. 34, 38, 39, 43, 46, 48, 49, 50.

Moreover, the diblends were also evaluated against a control Formulation No. 59 (see Table 9A), a 50/50 blend of Iotek 959/960, the best available high acid blends, with respect to improved C.O.R. values (i.e. 811/0.818). Similar or enhanced C.O.R. values (molded/finished) were observed in Formulation Nos. 31 (Na/Mn), 32 (Na/Li), 34 (Na/Zn), 35 (Na/Mg), 36 (Na/Ca), 38 (Mn/K), 43 (Li/Zn), 44 (Li/Mg), 45 (Li/Ca), and 47 (K/Mg).

Furthermore, when reviewed for cold cracking, with the exception of Formulation No. 35, all of the diblends tested exhibited resistance to breaking. With respect to Formulation No. 35, some breakage did occur with 2 out of the 12 balls tested exhibiting breakage.

When the small test sample of the triblends were evaluated (see Table 10 below) in comparison to a 50/50 blends of the low acid acrylic acid based hard ionomers (i.e. Iotek 8000/7030 U.S. Pat. No. 4,911,451), all of the cation neutralized high acid acrylic acid based triblends produced enhanced C.O.R. values upon molding and finishing. In addition, when subjected to cold cracking, no breakages were observed.

                  TABLE 10                                                         ______________________________________                                                                C.O.R.   C.O.R.                                         Formulation                                                                             Cation Blend  Molded   Finished Ball                                  ______________________________________                                         62       Zn/Li/K       .819     .828                                           63       Na/Zn/Li      .821     .829                                           64       Iotek 8000/7030                                                                              .816     .819                                           65       Na/Mn/Ca      .820     .828                                           66       Na/K/Mn       .821     .829                                           67       Na/K/Mg       .821     .829                                           ______________________________________                                    

Consequently, not only are a number of new cation neutralized acrylic acid based high acid ionomers now available for golf ball cover construction, these new cation neutralized acrylic acid based high acid ionomers may be blended together in various combinations to produce cover compositions exhibiting enhanced resilience (i.e. distance) due to the synergies noted above.

EXAMPLE 2

In order to determine whether the diblends or triblends of the new cation neutralized acrylic acid based high acid ionomer resins produced different results when dry blended (i.e. prepared as simple dry blends of pre-made single cation neutralized acrylic acid based high acid ionomers, such as those set forth in Example 1 above) or when produced as "in-situ" cation blends (i.e. the cations were first blended and then added to the acrylic acid/ethylene copolymers in the Banbury mixer), a number of comparison reactions were generated. Specifically, in-situ Formulation Nos. 68-72 in Table 11 below correspond to dry-blended Formulation Nos. 31, 32, 43, 44 and 46, respectively, and in-situ Formulation Nos. 73 and 74 in Table 11 below correspond to dry-blended Formulation Nos. 62 and 63, respectively.

                                      TABLE 11                                     __________________________________________________________________________                        C.O.R.                                                                              C.O.R.                                                                              Spin Rate                                                                             Shore D                                    Formulation No.                                                                          Cation Blend                                                                            Molded                                                                              Finished                                                                            9-Iron.RPM                                                                            Hardness                                   __________________________________________________________________________     68        Na/Mn    .822 .828 5,008  74                                         69        Na/Li    .820 .828 5,820  70                                         70        Li/Zn    .820 .825 5,425  71                                         71        Li/Mg    .821 .828 5,451  73                                         72        Zn/K     .817 .821 5,934  69                                         73        Li/Zn/K  .822 .826 5,266  71                                         74        Na/Li/Zn .821 .824 5,165  71                                         75        Iotek    .819 .824 5,926                                                       959(Na)/960(Zn)                                                      Tour Edition ® 100       10,124                                            Tour Edition ® 90        9,821                                             Top-Flite ® XL II        6,942                                             __________________________________________________________________________

The results indicated that little difference in C.O.R. was produced (relative to a control of 50/50 mixture of the high acid Iotek 959/960) whether a dry blending process or an in-situ blending process was used. Moreover, the data further clearly indicated that the cation neutralized acrylic acid based high acid ionomer blends of the present invention generally exhibit higher C.O.R. values and significantly lower spin rates than the best acrylic acid based high acid ionomers (i.e. the Ioteks 959(Na)/960(Zn) blend), see Formulation Nos. 68, 70, 71, 73 and 74 in comparison to Formulation No. 75 (control). The lower C.O.R. value and the substantially similar spin rate produced by the Zn/K blend in Formulation 72 was attributed to the slightly lower hardness of this blend versus the others. As indicated in Table 8, the K and Zn acrylic acid based high acid ionomers are a little softer than the Na, Mn, Li and Mg acrylic acid based high acid ionomers. Similarly, the higher spin rate of the Na/Li blend in Formulation 69 was due to its relative softness versus the other blends. In addition, other more subtle factors may also be at play, such as differences in coefficient of friction, deformation under load, etc., which have not quantified.

In addition, when compared with a number of commercially available balls produced by Spalding & Evenflo Companies, Inc., the assignee of the present invention, with low acid ionomer resin covers (i.e. the Tour Edition® 100, Tour Edition® 90 and Top-Flite® XL II balls), the spin rates of the cation neutralized acrylic acid high acid ionomer blends of the present invention (i.e. Formulations 68-75) exhibited much lower spin rates. Consequently, the cation neutralized acrylic acid based high acid ionomer blends of the present invention produced, when utilized to formulate the cover of a multi-layered golf ball, a much harder surface then those produced by the low acid ionomer covers presently available. This may be desirable to a golfer who imparts unmanageable spin (slice/hook) to the ball and therefore may benefit from a "low spin" ball.

EXAMPLE 3 Acrylic Acid Based High Acid Ionomer Di-Blends Containing Varying Ratios of Cation Neutralized Acrylic Acid Based High Acid Ionomers

In addition to the 50/50 blends of various combinations of the new cation neutralized acrylic acid based high acid ionomers set forth in Example 1, di-blends varying from 25/75 to 75/25 ratios were produced utilizing the more preferred diblends in the "in-situ" process described in Example 2. In this regard, the more preferred diblend formulations set forth in Example 1 (i.e. Formulation No. 31 (Na/Mn), Formulation No. 32 (Na/Li), Formulation 43 (Li/Zn), Formulation No. 44 (Li/Mg), and Formulation No. 46 (Zn/K)) were produced in-situ in 50/50, 25/75 and 75/25 combinations according to the following formulations:

                                      TABLE 12                                     __________________________________________________________________________     Formulations                                                                   __________________________________________________________________________     Ingredients                                                                               76 77 78 79 80 81 82  83 84 85                                      __________________________________________________________________________     Acid Copolymer                                                                            100                                                                               100                                                                               100                                                                               100                                                                               100                                                                               100                                                                               100 100                                                                               100                                                                               100                                     (Primacor 5981)                                                                NaOH       2.0                                                                               1.0                                                                               3.0                                                                               2.0                                                                               1.0                                                                               3.0                                                                               --  -- -- --                                      Mn Acetate 15.0                                                                              22.5                                                                              7.5                                                                               -- -- -- --  -- -- --                                      Lithium Hydroxide                                                                         -- -- -- 3.1                                                                               4.7                                                                               1.6                                                                               3.1 1.6                                                                               4.7                                                                               3.1                                     Monohydrate                                                                    Zinc Acetate                                                                              -- -- -- -- -- -- 8.00                                                                               12.0                                                                              4.0                                                                               --                                      Potassium Hydroxide                                                                       -- -- -- -- -- -- --  -- -- --                                      Magnesium Acetate                                                                         -- -- -- -- -- -- --  -- -- 10.5                                    __________________________________________________________________________                Formulation No.                                                     Ingredients                                                                               86      87 88      89  90                                           __________________________________________________________________________     Primacor 5981                                                                             100     100                                                                               100     100 100                                          Lithium Hydroxide                                                                         1.6     4.7                                                                               --      --  --                                           Magnesium Acetate                                                                         15.8    5.3                                                                               --      --  --                                           Zinc Acetate                                                                              --      -- 8.00    12.0                                                                               4.0                                          Potassium Hydroxide                                                                       --      -- 4.50    2.25                                                                               6.75                                         __________________________________________________________________________

The di-blends produced the following C.O.R. values:

                  TABLE 13                                                         ______________________________________                                         Formulation No.                                                                              Cation Blend                                                                              C.O.R. (Molded)                                       ______________________________________                                         76            50/50 Na/Mn                                                                               .820                                                  77            25/75 Na/Mn                                                                               .821                                                  78            75/25 Na/Mn                                                                               .825                                                  79            50/50 Na/Li                                                                               .822                                                  80            25/75 Na/Li                                                                               .822                                                  81            75/25 Na/Li                                                                               .823                                                  82            50/50 Li/Zn                                                                               .816                                                  83            25/75 Li/Zn                                                                               .804                                                  84            75/25 Li/Zn                                                                               .825                                                  85            50/50 Li/Mg                                                                               .823                                                  86            25/75 Li/Mg                                                                               .822                                                  87            75/25 Li/Mg                                                                               .821                                                  88            50/50 Zn/K .820                                                  89            75/25 Zn/K .798                                                  90            25/75 Zn/K .821                                                  ______________________________________                                          Control is a 50/50 Iotek Low Acid Ionomer Blend (8000/7030), C.O.R.            (molded) .817                                                            

The results indicated that in general the new cation neutralized acrylic acid based high acid ionomer diblends produced enhanced C.O.R. values over the known acrylic acid based low acid ionomer blends. See Formulation Nos. 76-81, 84-88 and 90. While Formulation 82 produced a lower C.O.R. value than expected, the data suggested that in some cases, a 50/50 blend is not optimal (particularly in the Zn/K and the Li/Zn blends), while in others (i.e. Li/Mg, Na/Li) the blend ratio is not significantly different.

EXAMPLE 4

Since the data set forth in Examples 1-3 indicated the resilience (C.O.R.) and/or hardness properties of the cover compositions can be substantially enhanced through the use of the new cation neutralized acrylic acid based high acid ionomers and/or diblends or triblends of such ionomers, the molecular weight property of the acrylic acid/ethylene copolymers utilized to produce the ionomers was evaluated. Specifically, the molecular weight of the acid copolymers was assessed for the purpose of determining whether further enhanced properties can be produced by varying the molecular weight of the acid copolymer.

In this regard, since the data indicated that there was little difference between using the dry blending process or the in-situ blending method for processing the cations, the in-situ method of producing the cation neutralized high acid ionomer blends was used in this analysis.

Along this line, the diblend and triblends set forth in Formulation Nos. 68, 73 and 74 are essentially the same as those set forth below in Formulation Nos. 91, 94 and 97, respectively. However, since a different batch of cores was utilized than those used in Example 2, the C.O.R.'s are slightly lower. While the cores utilized in the present Example were of the same composition, the lower C.O.R. was due to the age of the cores, i.e. molded cores will lose C.O.R. upon aging mainly due to moisture pickup. Formulation Nos. 92-93, 95-96 and 98-99, are similar to those set forth in Formulation Nos. 91, 94 and 97, respectively, with the exception that the molecular weight of the acrylic acid/ethylene copolymer utilized was varied. Specifically, Primacor 5983 and Primacor 5990 both contain the same acid content as Primacor 5981 (i.e. 20 weight percent acrylic acid) but have lower viscosities (lower molecular weights) and lower densities. Primacor 5981 has a melt index of 300 g/10 minute (ASTM Method D-1238 at 190° C.) and a Brookfield viscosity of 51,000 cps at 350° F. Primacor 5983 has a melt index of 500 and a Brookfield viscosity of 26,000 cps at 350° F.; and Primacor 5990 has a melt index of 1300 and viscosity of 13,000 cps at 350° F.

The resilience (C.O.R.) of the molded balls produced utilizing the different molecular weight acrylic acid/ethylene copolymers are set forth below in Table 14.

                  TABLE 14                                                         ______________________________________                                         Formulation                      C.O.R.                                        No.      Cations    Acid Copolymer                                                                              (MOLDED)                                      ______________________________________                                         91       Na/Mn      Primacor 5981                                                                               .813                                          92       Na/Mn      Primacor 5983                                                                               .805                                          93       Na/Mn      Primacor 5990                                                                               All Balls crack                               94       Li/Zn/K    Primacor 5981                                                                               .814                                          95       Li/Zn/K    Primacor 5983                                                                               .809                                          96       Li/Zn/K    Primacor 5990                                                                               All Balls crack                               97       Na/Li/Zn   Primacor 5981                                                                               .813                                          98       Na/Li/Zn   Primacor 5983                                                                               .808                                          99       Na/Li/Zn   Primacor 5990                                                                               All Balls crack                               ______________________________________                                    

The data indicated that a higher molecular weight acid copolymer is preferred for obtaining high resilience (i.e. C.O.R.) and required toughness.

EXAMPLE 5

By way of further example, golf ball cover compositions were prepared by first blending an acid copolymer such as ethylene acrylic acid copolymer (EAA) with a non-acid functional polymer such as ethylene-ethyl acrylate (EEA) and/or ethylene-methyl acrylate (EMA). This was followed by addition of a cation or cation blend for neutralization. Selection of the type and ratio of acid copolymer to EEA or EMA was based upon the desired final properties of the ball such as hardness or spin rate. Tables 15-17 show the compositions and properties of balls having covers prepared using ethylene acrylates, and Table 18 shows the properties of several golf balls produced by the present assignee which do not contain ethylene acrylates but exhibit somewhat similar properties.

Table 15 below provides for the results of simple blends of ionomers with various non-acid functional polymers. Iotek's 959 and 960 were selected for their similarity in properties to ionomers made from Primacor 5981.

                                      TABLE 15                                     __________________________________________________________________________     Formulation No.                                                                           100 101 102 103 104 105 106 107                                     __________________________________________________________________________     Iotek 959  50  25  25  25  25  25  25  25                                      Iotek 960  50  25  25  25  25  25  25  25                                      Kraton FG-1901X                                                                           --  50  --  --  --  --  --  --                                      EEA 6169   --  --  50  --  --  --  --  --                                      EEA 6182   --  --  --  50  --  --  --  --                                      EMA 53.04  --  --  --  --  50  --  --  --                                      EMA XS 12.04                                                                              --  --  --  --  --  50  --  --                                      EMA TC-130 --  --  --  --  --  --  50  --                                      Fusabond D-197                                                                            --  --  --  --  --  --  --  50                                      Compression                                                                               56  59  61  60  61  61  63  60                                      Molded COR .818                                                                               .797*                                                                              .797                                                                               .798                                                                               .797                                                                               .798                                                                               .793*                                                                              .796                                    Finished COR                                                                              .821                                                                               .798                                                                               .795                                                                               .798                                                                               .797                                                                               .799                                                                               .787                                                                               .796                                    Shore C Hardness                                                                          98  85  86  88  80  85  80  88                                      Cut Resistance                                                                            4-5 3   2-3 2   2   2   2   2                                       Spin Rate (full 9 iron)                                                                   5,969                                                                              9,495                                                                              8,997                                                                              9,260                                                                              9,145                                                                              9,732                                                                              9,857                                                                              9,340                                   __________________________________________________________________________      *Several balls cracked on Formulations 101 and 106 during COR testing.   

Blends similar to those of Table 15 were prepared using Primacor 5981 as the acid copolymer of choice instead of Iotek 959/960. These blends, and the resulting properties, are set forth below in Table 16:

                                      TABLE 16                                     __________________________________________________________________________     Formulation No.                                                                            108 109 110 111 112 113 114 115                                    __________________________________________________________________________     Primacor 5981                                                                              100 50  50  50  50  50  50  50                                     Nucrel 960  --  --  --  --  --  --  --  --                                     Kraton FG-1901X                                                                            --  50  --  --  --  --  --  --                                     EEA 6169    --  --  50  --  --  --  --  --                                     EEA 6182    --  --  --  50  --  --  --  --                                     EMA 53.04   --  --  --  --  50  --  --  --                                     EMA X512.04 --  --  --  --  --  50  --  --                                     EMA TC-130  --  --  --  --  --  --  50  --                                     Fusabond D-197                                                                             --  --  --  --  --  --  --  50                                     Zinc Acetate                                                                               5.33                                                                               5.33                                                                               5.33                                                                               5.33                                                                               5.33                                                                               5.33                                                                               5.33                                                                               5.33                                   Potassium Hydroxide                                                                        3.00                                                                               3.00                                                                               3.00                                                                               3.00                                                                               3.00                                                                               3.00                                                                               3.00                                                                               3.00                                   Lithium Hydroxide                                                                          2.05                                                                               2.05                                                                               2.05                                                                               2.05                                                                               2.05                                                                               2.05                                                                               2.05                                                                               2.05                                   Compression 55  62  60  60  63  63  62  62                                     Molded COR  .820                                                                               .802                                                                               .792                                                                               .794                                                                               .791                                                                               .790                                                                               .793                                                                               .802                                   Finished COR                                                                               .825                                                                               .802                                                                               .792                                                                               .796                                                                               .793                                                                               .790                                                                               .794                                                                               .801                                   Shore C Hardness                                                                           98  90  86  90  77  83  83  88                                     Cut Resistance                                                                             4-5 3   3   3   2   3   2   3-4                                    Spin Rate (Full 9 Iron)                                                                    5,787                                                                              8,834                                                                              9,232                                                                              9,148                                                                              10,220                                                                             9,516                                                                              9,552                                                                              9,091                                  __________________________________________________________________________

While Primacor 5981 has been the acid copolymer of choice herein as a result of its high COR, it should be noted that lower acid copolymers or a blend of acid copolymers may be used with satisfactory results. Table 17 below shows several compositions using lower acid copolymers or a blend of acid copolymers, along with the resulting properties of the finished cover and ball.

                  TABLE 17                                                         ______________________________________                                         Formulation No.                                                                              116    117     118   119   120                                   ______________________________________                                         Primacor 5981 --     --      --    25    --                                    Nucrel 960    50     50      50    25    100                                   Kraton FG-1901X                                                                              --     --      --    --    --                                    EEA 6169      --     --      --    --    --                                    EEA 6182      50     --      --    --    --                                    EMA 53.04     --     50      --    50    --                                    EMA X512.04   --     --      --    --    --                                    EMA TC-130    --     --      --    --    --                                    Fusabond D-197                                                                               --     --      50    --    --                                    Zinc Acetate  4.00   4.00    4.00  4.70  4.00                                  Potassium Hydroxide                                                                          2.27   2.27    2.27  2.60  2.27                                  Lithium Hydroxide                                                                            1.50   1.50    1.50  1.80  1.50                                  Compression   68     66      64    64    58                                    Molded COR    .793   .789    .800  .790  .813                                  Finished COR  .793   .788    .798  .790  .815                                  Shore C Hardness                                                                             86     75      88    76    96                                    Cut Resistance                                                                               3      3       3     3     4                                     Spin Rate (Full 9 Iron)                                                                      9,436  10,306  9,315 10,168                                                                               7,014                                 ______________________________________                                    

One of the objectives in preparing the formulations listed in Tables 15-17 was to make a soft covered golfball having properties similar to the current "Tour" balls of the present assignee. The properties of the subject assignee's Titleist Tour 100, Tour Edition 100, Tour Edition 90, and Top-Flite XL II are provided in Table 18. These properties may be compared with those listed in Tables 15-17 to find many similarities such that a lower cost alternative may be provided.

                  TABLE 18                                                         ______________________________________                                                             Tour    Tour    Top-                                                    Titleist                                                                              Edition Edition Flite XL                                                Tour 100                                                                              100     90      II                                         ______________________________________                                         Compression    75       57      55    47                                       Molded COR     --       --      --    --                                       Finished COR   .786     .809    .813  .814                                     Shore C Hardness                                                                              82       84      86    96                                       Cut Resistance 1        3       3     4-5                                      Spin Rate (Full 9 Iron)                                                                       9,422    9,924   9,703 6,968                                    ______________________________________                                    

Little is known of the reaction mechanism or to what extent the EEA and/or EMA actually take part in the reaction of EEA/EMA with an acid copolymer and the addition of a cation or cation blend for neutralization. There is, however, some belief that there is at least enough interaction between polymers to provide a net benefit in properties versus a simple blend of an ionomer and EEA/EMA. It is possible that an interpenetrating polymer network (IPN) is formed by reacting (neutralizing) the acid copolymer in the presence of EEA/EMA. By first forming an intimate blend of polymers and then neutralizing one in the presence of another it is possible that a network is formed via intermolecular chain entanglement of the two polymers.

It is also possible that a dynamic vulcanization takes place where superior properties are the result of a finer phase morphology of the dispersed crosslinked phase (here, the neutralized acid copolymer) in an essentially uncrosslinked continuous matrix of ethylene acrylate ester.

The formations of Tables 15-17 above include examples of an acid copolymer reacted in the presence of maleic anhydride functional elastomers Kraton FG-1901X and Fusabond D-197. In simple blends with ionomers, this was the subject of U.S. Pat. Nos. 4,986,545 and 5,098,105, incorporated herein by reference.

A further advantage of the reactive blends of Tables 16 and 17 over the non-reactive blends of Table 15 is the improved cut resistance. While most of the blends of Table 15 give an undesirable "2" rating, nearly all of those in Tables 16 and 17 give a rating of "3", which is comparable to the current Tour balls (see, e.g. Table 18). It should be further noted that formulations 101 and 106 in Table 15 had several balls break during COR testing. The related formulations in Table 16 (formulations 109 and 114) did not have this problem. In general, although no COR advantage is observed (i.e., some COR values of Table 16 are higher and some are lower than the corresponding Table 15 formulations) the balls prepared using the formulations of Table 16 are tougher, slightly softer and more durable than those of Table 15.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such alterations and modifications insofar as they come within the scope of the appended claims or the equivalents thereof. 

We claim:
 1. A golf ball having a core and a cover wherein said cover comprises 30 to 90% of a neutralized ethylene/acrylic acid copolymer and 10-70 parts by weight of an ethylene alkyl acrylate copolymer containing up to 30% by weight of the alkyl acrylate.
 2. A golf ball, as set forth in claim 1, wherein the cover comprises about 40 to 80 parts by weight of an acid copolymer and about 20 to 60 parts by weight of an ethylene copolymer.
 3. A golf ball, as set forth in claim 1, wherein the cover comprises about 50 to 70 parts by weight of an acid copolymer and about 30 to 50 parts by weight of an ethylene copolymer.
 4. A golf ball, as set forth in claim 1, wherein the acid copolymer includes about 1% to about 25% by weight of an alpha, beta unsaturated carboxylic acid.
 5. A golf ball, as set forth in claim 1, wherein the ethylene copolymer is ethylene ethyl acrylate.
 6. A golf ball, as set forth in claim 1, wherein the ethylene copolymer is ethylene methyl acrylate.
 7. A golf ball, as set forth in claim 1, wherein the ethylene copolymer is ethylene butyl acrylate.
 8. A golf ball, as set forth in claim 1, further including up to about 11 parts by weight of an acetate or hydroxide salt of a member selected from the group consisting of zinc, potassium, lithium, calcium, sodium, nickel, magnesium, and manganese, said acetate or hydroxide salt providing a source for the neutralizing metal cation.
 9. A golf ball having a core and cover wherein the cover comprises of a neutralized acrylic, acid/ethylene copolymer having from about 9 to about 25% acrylic acid and 10-70 parts by weight of an ethylene/alkyl acrylate copolymer containing up to 30% of an alkyl acrylate selected from the group consisting of methyl acrylate, butyl acrylate, and ethyl acrylate.
 10. A golf ball comprising a core and a cover wherein said cover comprises 30 to 90 parts by weight of a 10 to 90% neutralized carboxylic acid/ethylene copolymer and 10 to 70 parts by weight of an ethylene/alkyl acrylate copolymer containing up to 30% by weight of the alkyl acrylate.
 11. A golf ball, as set forth in claim 10, wherein the carboxylic acid is acrylic acid.
 12. A golf ball, as set forth in claim 10, wherein the metal cation is selected from the group consisting of zinc, potassium, lithium, calcium, sodium, nickel, magnesium, and manganese.
 13. A golf ball, as set forth in claim 12, wherein the alkyl acrylate is selected from the group consisting of butyl acrylate, methyl acrylate, and ethyl acrylate.
 14. A golf ball, as set forth in claim 12, wherein the cover comprises about 40 to 80 parts by weight of an acid copolymer and about 20 to 60 parts by weight of an ethylene copolymer.
 15. A golf ball, as set forth in claim 12, wherein the cover comprises about 50 to 70 parts by weight of an acid copolymer and about 30 to 50 parts by weight of an ethylene copolymer. 